The candidate's long term goals are to understand how neuronal fate becomes specified and how neurons find and recognize their appropriate synaptic partners during development. The goal of the current application is two-fold: 1) to examine how environmental cues guide the growth cones of identified neurons to cell-specific targets during development and 2) to enable the candidate to learn and implement molecular and genetic approaches in her lab. These new approaches will complement the cellular approach currently used in the candidate's lab by allowing her to address both the phenomenology and the mechanisms of neuronal developmental. The candidate is fortunate to work in the University of Oregon Institute of Neuroscience, where she has daily interactions with other labs that also investigate neuronal development. The Institute is very supportive of her desire to receive additional training so that she can broaden her research, and she has received a commitment for a reduction in teaching and other academic responsibilities if she receives this award. The proposed studies will be carried out in a simple vertebrate, the embryonic zebrafish, where individual neurons can be identified and their development observed directly in living embryos. The candidate proposes to examine whether target muscles produce permissive signals that promote elongation of the growth cones of all motoneurons or instructive signals that guide the growth cones of particular motoneurons as they pioneer cell-specific pathways to cell-specific targets. The relationship between identified motoneurons and their target muscles will be altered by transplanting muscle precursors and motoneurons, and the subsequent pathway choices made by the growth cones of identified motoneurons will be observed in living embryos. The candidate proposes to compare the pathfinding abilities of two populations of motoneurons that develop at different times, to learn whether their growth cones use different cues to reach the same target muscle. Pioneering motoneurons will be ablated using laser-irradiation to learn whether their presence is required for proper pathfinding by follower motoneurons. The candidate proposes to use genetic and molecular approaches to isolate putative guidance molecules and study the mechanisms by which they direct pathfinding, and to study the mechanisms underlying the specification of neuronal fate.